The invention relates to an implant for internal fixation of bone and in particular to an implant for internal fixation of diaphyseal and multi-part fractures of the humerus to promote osteosynthesis. The invention can be used, for example, in conjunction with an intramedullary device containing a proximal slot for the humeral spiral blade to be positioned and provisionally locked.
Overall between 160,000 and 180,000 individuals suffer fractures of the humerus each year. Approximately seventy five percent of fractures occur in the proximal region of the humerus near the head or cortex, ten percent occur in the mid-shaft region, and fifteen percent occur in the distal region of the humerus.
Diaphyseal humeral fractures involve the humeral shaft. Proximal humeral fractures involve fractures of the head or cortex and often result from a fall that places an axial load on the humerus. In a two-part fracture, the head or a single portion of the head is broken from the humeral shaft. Multi-part fractures involve fracture of the humeral head into two or three fragments that separate from the shaft.
Conventional treatment of diaphyseal and multi-part humeral fractures often involves wiring, suturing, or externally fixing the fragments to one another and/or the humeral shaft. Other known approaches involve inserting one or more screws into the head or shaft of the humerus and fixing the nails or screws to a nail inserted into the medullary canal of the humerus, such as those described in U.S. Pat. Nos. 4,503,847, 5,472,444, 5,697,930, and 5,766,174.
Frequent postoperative complications arise when two or more of the bone fragments are forced together as when the patient applies pressure to the healing bone. For example, a sharp implanted nail or screw may cut out and through the humeral head or neck; or a nail, screw, or intramedullary nail may bend or break under a load. Cut out is particularly problematic in individuals with poor bony stock, such as cancerous or osteoporotic bone. A need exists, therefore, to provide improved osteosynthetic implants for treatment of multi-part and diaphyseal fractures of the humerus.
Femoral fractures have been treated using single, helical blades, such as disclosed in U.S. Pat. Nos. 4,103,683, 4,978,349, and 5,300,074. These blades are twisted about ninety degrees along their length and have a generally flat rectangular profile with a substantially uniform width and narrow thickness. When implanted in conjunction with an intramedullary nail, these blades are oriented to reduce pressure on cancellous tissue within the femoral head and to provide a high resistance to bending in response to loads along the longitudinal axis of the intramedullary nail.
Because of the aforementioned narrow thickness, however, the prior art single helical femoral blades are fairly compliant in the transverse direction, i.e., in the anterior and posterior directions of the patient. Moreover, the overall flat profile of the blades provides little resistance to cutting through the cancellous bone like a knife in directions aligned with the width of the blade at any station along its length. A need exists, therefore, to provide improved osteosynthetic implants for treatment of multi-part and diaphyseal fractures of the humerus which do not have a tendency to cause such cutting and provides greater resistance to bending in the transverse direction.
Repairing a fractured humerus frequently involves repair of damaged soft tissue surrounding the humerus. Traditional suture anchors suffer from pullout in weakened bone and also require that additional holes be drilled in an already weakened humerus. U.S. Pat. No. 5,766,174 discloses an intramedullary nail having suture holes and a nail cap with suture holes. Suture holes on an intramedullary nail are often not accessible once the nail has been implanted in a fractured humerus. Thus, in repair of a fractured humerus, a need also exists to provide robust, accessible sites for suture attachment that do not require additional drilling of the fractured humerus.
The present invention relates to an implant for a bone. The implant has a body member having a lateral portion, a medial portion, and a helically twisted blade extending along the body and having a longitudinal axis. In a preferred embodiment, the lateral portion of the helically twisted blade is twisted about one fourth turn with respect to the medial portion.
The lateral portion of the body has a circumferential collar extending in a plane perpendicular to the longitudinal axis. The circumferential collar has an attachment element for attaching a tissue fastener for repairing tissue surrounding the bone. In one embodiment, the attachment element comprises a hole for securing the tissue fastener. In another embodiment, the attachment element comprises a threaded hole.
In another embodiment, the body member has a central portion between the lateral and medial portions. The central portion has a cross section and a maximum thickness adjacent the longitudinal axis which gradually tapers to a minimum thickness apart from the longitudinal axis.
In a preferred embodiment, a cannulation extends through the body member along the longitudinal axis from the medial portion to the lateral portion. In another embodiment, the circumferential collar includes a central hole configured with threads to releasably engage a tool for positioning the invention in the bone.
In another embodiment, the medial portion has a medially extending medial end portion having surfaces configured for cutting through the bone. In a preferred embodiment, the medial end portion includes first and second cutting regions and a transverse axis. The first and second cutting regions are asymmetrically disposed about the transverse axis. In a preferred embodiment, the first and second cutting regions further include cutting edges, which form an angle of about thirty degrees to the transverse axis. The first and second cutting regions may include an angled cutting surface. In a preferred embodiment, the angled cutting surfaces form an angle of from about five to sixty degrees with respect to the longitudinal axis.
The present invention also relates to an osteosynthetic apparatus for fixing a broken humerus. The apparatus includes the implant of the present invention and a securing member comprising an elongated nail having a proximal securing portion configured to occupy a proximal portion of the humeral shaft and a distal portion configured to occupy a distal portion of the humeral shaft. In a preferred embodiment, the proximal securing portion has at least one longitudinal bore configured to accommodate the implant. When the implant is accommodated by the longitudinal bore, a medial portion of the implant is preferably within the head of the humerus and the implant may be positioned and provisionally locked.
The present invention further relates to a method for fixing a broken humerus. The method includes implanting the implant of the present invention in the humerus with the medial portion of the twisted blade inside the head of the humerus. In a preferred embodiment, the circumferential collar of the implant include a plurality of holes.